Heretofore, most wells drilled in the earth to produce oil, gas and other minerals therefrom have been drilled essentially vertically so that the wellbores penetrate the mineral producing formation essentially at right angles although not precisely at right angles because the producing formation may dip from horizontal from place to place. However, the point is that the wellbores were essentially deliberately drilled vertically and in many situations, a lot of effort was put into the drilling procedure to insure that the wellbore remained essentially vertical rather than deviating to any substantial degree to an angle from vertical.
Deviated wellbores have been drilled, particularly in offshore applications, which do curve at an angle from vertical, but no particular effort has been put into the drilling procedure to insure that the wellbores penetrated the producing formation in a systematic fashion at an angle from vertical. In fact, a particular species of deviated wellbore, known as drainhole wellbores, deliberately turns essentially a 90 degree angle from vertical at or in the producing formation so that the wellbore can be extended essentially horizontally away from the vertical primary wellbore as to stay within the producing formation. The drainhole wellbore is then drilled horizontally out into the producing formation as far as possible.